The present invention relates to fuels for transportation which are liquid at ambient conditions, and are typically derived from natural petroleum. Broadly, it relates to integrated, multiple stage processes for producing products of reduced sulfur content from a feedstock wherein the feedstock is comprised of limited amounts of sulfur-containing organic compounds as unwanted impurities. More particularly, the invention relates to a multiple stage process for converting these impurities to higher boiling products by alkylation and removing the higher boiling products by fractional distillation. Integrated processes of this invention advantageously include selective hydrogenation of the high-boiling fraction whereby the incorporation of hydrogen into hydrocarbon compounds, sulfur-containing organic compounds, and/or nitrogen-containing organic compounds assists by hydrogenation removal of sulfur and/or nitrogen. Products can be used directly as transportation fuels and/or blending components to provide fuels which are more friendly to the environment.
It is well known that internal combustion engines have revolutionized transportation following their invention during the last decades of the 19th century. While others, including Benz and Gottleib Wilhelm Daimler, invented and developed engines using electric ignition of fuel such as gasoline, Rudolf C. K. Diesel invented and built the engine named for him which employs compression for auto-ignition of the fuel in order to utilize low-cost organic fuels. Equal, if not more important, development of improved spark-ignition engines for use in transportation has proceeded hand-in-hand with improvements in gasoline fuel compositions. Modern high performance gasoline engines demand ever more advanced specification of fuel compositions, but cost remains an important consideration.
At the present time most fuels for transportation are derived from natural petroleum. Indeed, petroleum as yet is the world""s main source of hydrocarbons used as fuel and petrochemical feedstock. While compositions of natural petroleum or crude oils are significantly varied, all crudes contain sulfur compounds and most contain nitrogen compounds which may also contain oxygen, but oxygen content of most crudes is low. Generally, sulfur concentration in crude is less than about 8 percent, with most crudes having sulfur concentrations in the range from about 0.5 to about 1.5 percent. Nitrogen concentration is usually less than 0.2 percent, but it may be as high as 1.6 percent.
Crude oil seldom is used in the form produced at the well, but is converted in oil refineries into a wide range of fuels and petrochemical feedstocks. Typically fuels for transportation are produced by processing and blending of distilled fractions from the crude to meet the particular end use specifications. Because most of the crudes available today in large quantity are high in sulfur, the distilled fractions must be desulfurized to yield products which meet performance specifications and/or environmental standards. Sulfur containing organic compounds in fuels continue to be a major source of environmental pollution. During combustion they are converted to sulfur oxides which, in turn, give rise to sulfur oxyacids and, also, contribute to particulate emissions.
In the face of ever-tightening sulfur specifications in transportation fuels, sulfur removal from petroleum feedstocks and products will become increasingly important in years to come. While legislation on sulfur in diesel fuel in Europe, Japan and the U.S. has recently lowered the specification to 0.05 percent by weight (max.), indications are that future specifications may go far below the current 0.05 percent by weight level. Legislation on sulfur in gasoline in the U.S. now limits each refinery to an average of 30 parts per million. In and after 2006 the average specification will be replaced by a cap of 80 parts per million maxim.
The fluidized catalytic cracking process is one of the major refining processes which is currently employed in the conversion of petroleum to desirable fuels such as gasoline and diesel fuel. In this process, a high molecular weight hydrocarbon feedstock is converted to lower molecular weight products through contact with hot, finely-divided, solid catalyst particles in a fluidized or dispersed state. Suitable hydrocarbon feedstocks typically boil within the range of 205xc2x0 C. to about 650xc2x0 C., and they are usually contacted with the catalyst at temperatures in the range 450xc2x0 C. to about 650xc2x0 C. Suitable feedstocks include various mineral oil fractions such as light gas oils, heavy gas oils, wide-cut gas oils, vacuum gas oils, kerosenes, decanted oils, residual fractions, reduced crude oils and cycle oils which are derived from any of these as well as fractions derived from shale oils, tar sands processing, and coal liquefaction. Products from a fluidized catalytic cracking process are typically based on boiling point and include light naphtha (boiling between about 10xc2x0 C. and about 221xc2x0 C.), heavy naphtha (boiling between about 10xc2x0 C. and about 249xc2x0 C.), kerosene (boiling between about 180xc2x0 C. and about 300xc2x0 C.), light cycle oil (boiling between about 221xc2x0 C. and about 345xc2x0 C.), and heavy cycle oil (boiling at temperatures higher than about 345xc2x0 C.).
Not only does the fluidized catalytic cracking process provide a significant part of the gasoline pool in the United States, it also provides a large proportion of the sulfur that appears in this pool. The sulfur in the liquid products from this process is in the form of organic sulfur compounds and is an undesirable impurity which is converted to sulfur oxides when these products are utilized as a fuel. These sulfur oxides are objectionable air pollutants. In addition, they can deactivate many of the catalysts that have been developed for the catalytic converters which are used on automobiles to catalyze the conversion of harmful engine exhaust emissions to gases which are less objectionable. Accordingly, it is desirable to reduce the sulfur content of catalytic cracking products to the lowest possible levels.
The sulfur-containing impurities of straight run gasolines, which are prepared by simple distillation of crude oil, are usually very different from those in cracked gasolines. The former contain mostly mercaptans and sulfides, whereas the latter are rich in thiophene, benzothiophene and derivatives of thiophene and benzothiophene.
Low sulfur products are conventionally obtained from the catalytic cracking process by hydrotreating either the feedstock to the process or the products from the process. Hydrotreating involves treatment of products of the cracking process with hydrogen in the presence of a catalyst and results in the conversion of the sulfur in the sulfur-containing impurities to hydrogen sulfide, which can be separated and converted to elemental sulfur. Unfortunately, this type of processing is typically quite expensive because it requires a source of hydrogen, high pressure process equipment, expensive hydrotreating catalysts, and a sulfur recovery plant for conversion of the resulting hydrogen sulfide to elemental sulfur. In addition, the hydrotreating process can result in an undesired destruction of olefins in the feedstock by converting them to saturated hydrocarbons through hydrogenation. This destruction of olefins by hydrogenation is usually undesirable because it results in the consumption of expensive hydrogen, and also because the olefins are valuable as high octane components of gasoline. As an example, naphtha of a gasoline boiling range from a catalytic cracking process has a relatively high octane number as a result of a large olefin content. Hydrotreating such a material causes a reduction in the olefin content in addition to the desired desulfurization, and the octane number of the hydrotreated product decreases as the degree of desulfurization increases.
Conventional hydrodesulfurization catalysts can be used to remove a major portion of the sulfur from petroleum distillates for the blending of refinery transportation fuels, but they are not efficient for removing sulfur from compounds where the sulfur atom is sterically hindered as in multi-ring aromatic sulfur compounds. This is especially true where the sulfur heteroatom is doubly hindered (e.g., 4,6-dimethyldibenzothiophene). Using conventional hydrodesulfurization catalysts at high temperatures would cause yield loss, faster catalyst coking, and product quality deterioration (e.g., color). Using high pressure requires a large capital outlay. Accordingly, there is a need for an inexpensive process for the effective removal of sulfur-containing impurities from distillate hydrocarbon liquids. There is also a need for such a process which can be used to remove sulfur-containing impurities from distillate hydrocarbon liquids, such as products from a fluidized catalytic cracking process, which are highly olefinic and contain both thiophenic and benzothiophenic compounds as unwanted impurities.
In order to meet stricter specifications in the future, such hindered sulfur compounds will also have to be removed from distillate feedstocks and products. There is a pressing need for economical removal of sulfur from refinery fuels for transportation, especially from components for gasoline.
The art is replete with processes said to remove sulfur from distillate feedstocks and products. For example, U.S. Pat. No. 6,087,544 in the name of Robert J. Wittenbrink, Darryl P. Klein, Michele S Touvelle, Michel Daage and Paul J. Berlowitz relates to processing a distillate feedstream to produce distillate fuels having a level of sulfur below the distillate feedstream. Such fuels are produced by fractionating a distillate feedstream into a light fraction, which contains only from about 50 to 100 ppm of sulfur, and a heavy fraction. The light fraction is hydrotreated to remove substantially all of the sulfur therein. The desulfurized light fraction, is then blended with one half of the heavy fraction to product a low sulfur distillate fuel, for example 85 percent by weight of desulfurized light fraction and 15 percent by weight of untreated heavy fraction reduced the level of sulfur from 663 ppm to 310 ppm. However, to obtain this low sulfur level only about 85 percent of the distillate feedstream is recovered as a low sulfur distillate fuel product.
U.S. Pat. No. 2,448,211, in the name of Philip D. Caesar, et al. states that thiophene and its derivatives can be alkylated by reaction with olefinic hydrocarbons at a temperature between about 140xc2x0 and about 400xc2x0 C. in the presence of a catalyst such as an activated natural clay or a synthetic adsorbent composite of silica and at least one amphoteric metal oxide. Suitable activated natural clay catalysts include clay catalysts on which zinc chloride or phosphoric acid have been precipitated. Suitable silica-amphoteric metal oxide catalysts include combinations of silica with materials such as alumina, zirconia, ceria, and thoria. U.S. Pat. No. 2,469,823, in the name of Rowland C. Hansford and Philip D. Caesar teaches that boron trifluoride can be used to catalyze the alkylation of thiophene and alkyl thiophenes with alkylating agents such as olefinic hydrocarbons, alkyl halides, alcohols, and mercaptans. In addition, U.S. Pat. No. 2,921,081, in the name of (Zimmerschied et al.) discloses that acidic solid catalysts can be prepared by combining a zirconium compound selected from the group consisting of zirconium dioxide and the halides of zirconium with an acid selected from the group consisting of ortho-phosphoric acid, pyrophosphoric acid, and triphosphoric acid. The Zimmerschied et al. reference also teaches that thiophene can be alkylated with propylene at a temperature of 227xc2x0 C. in the presence of such a catalyst.
U.S. Pat. No. 2,563,087 in the name of Jerome A. Vesely states that thiophene can be removed from aromatic hydrocarbons by selective alkylation of the thiophene and separation of the resulting thiophene alkylate by distillation. The selective alkylation is carried out by mixing the thiophene-contaminated aromatic hydrocarbon with an alkylating agent and contacting the mixture with an alkylation catalyst at a carefully controlled temperature in the range from about xe2x88x9220xc2x0 C. to about 85xc2x0 C. It is disclosed that suitable alkylating agents include olefins, mercaptans, mineral acid esters, and alkoxy compounds such as aliphatic alcohols, ethers and esters of carboxylic acids. It is also disclosed that suitable alkylation catalysts include the following: (1) the Friedel-Crafts metal halides, which are preferably used in anhydrous form; (2) a phosphoric acid, preferably pyrophosphoric acid, or a mixture of such a material with sulfuric acid in which the volume ratio of sulfuric to phosphoric acid is less than about 4:1; and (3) a mixture of a phosphoric acid, such as ortho-phosphoric acid or pyrophosphoric acid, with a siliceous adsorbent, such as kieselguhr or a siliceous clay, which has been calcined to a temperature of from about 400xc2x0 to about 500xc2x0 C. to form a silico-phosphoric acid combination which is commonly referred to as a solid phosphoric acid catalyst.
U.S. Pat. No. 3,894,941 in the name of Paul G. Bercik and Kirk J. Metzger describes a method for converting mercaptans to alkyl sulfides, sweet organic sulfides, by contacting the mercaptan-containing hydrocarbon feed having from 3 to 12 carbon atoms per molecule and free of hydrogen sulfide, with a tertiary olefin of a select group, in the presence of a catalyst comprising Group VI-B or Group VIII metals and a support consisting of semi-crystalline aluminosilicates and amorphous silica-aluminas. The patent states that concentrations of tertiary olefin in the conversion zone are in the range of 0.1 to 20 liquid volume percent. While the product is said to be substantially free of mercaptans, the level of elemental sulfur his not been reduced by this method.
U.S. Pat. No. 4,775,462 in the name of Tamotsu Imai and Jeffery C. Bricker describes a method a non-oxidative method of sweetening a sour hydrocarbon fraction whereby mercaptans are converted to thioethers which are said to be acceptable in fuels. The method involves contacting a mercaptan-containing hydrocarbon fraction with a catalyst consisting of an acidic inorganic oxide, a polymeric sulfonic acid resin, an intercalate compound, a solid acid catalyst, a boron halide dispersed on alumina, or an aluminum halide dispersed on alumina, in the presence of an unsaturated hydrocarbon equal to the molar amount of mercaptans, typically from about 0.01 weight percent to bout 20 weight percent. While the product is said to be substantially free of mercaptans, the level of elemental sulfur his not been reduced by this process.
U.S. Pat. No. 5,171,916 in the name of Quany N. Le and Michael S. Sarli describes a process for upgrading a light cycle oil by: (A) alkylating the heteroatom containing aromatics of the cycle oil with an aliphatic hydrocarbon having 14 to 24 carbon atoms and at least one olefinic double bond through the use of a crystalline metallosilicate catalyst; and (B) separating the high boiling alkylation product in the lubricant boiling range from the unconverted light cycle oil by fractional distillation. It also states that the unconverted light cycle oil has a reduced sulfur and nitrogen content, and the high boiling alkylation product is useful as a synthetic alkylated aromatic lubricant base stock.
U.S. Pat. No. 5,599,441 in the name of Nick A. Collins and Jeffrey C. Trewella describes a process for removing thiophenic sulfur compounds from a cracked naphtha by: (A) contacting the naphtha with an acid catalyst to alkylate the thiophenic compounds using the olefins present in the naphtha as an alkylating agent; (B) removing an effluent stream from the alkylation zone; and (C) separating the alkylated thiophenic compounds from the alkylation zone effluent stream by fractional distillation. It also states that additional olefins can be added to the cracked naphtha to provide additional alkylating agent for the process.
More recently, U.S. Pat. No. 6,024,865 in the name of Bruce D. Alexander, George A. Huff, Vivek R. Pradhan, William J. Reagan and Roger H. Cayton disclosed a product of reduced sulfur content which is produced from a feedstock which is comprised of a mixture of hydrocarbons and includes sulfur-containing aromatic compounds as unwanted impurities. The process involves separating the feedstock by fractional distillation into a lower boiling fraction which contains the more volatile sulfur-containing aromatic impurities and at least one higher boiling fraction which contains the less volatile sulfur-containing aromatic impurities. Each fraction is then separately subjected to reaction conditions which are effective to convert at least a portion of its content of sulfur-containing aromatic impurities to higher boiling sulfur-containing products by alkylation with an alkylating agent in the presence of an acidic catalyst. The higher boiling sulfur-containing products are removed by fractional distillation. It is also stated that alkylation can be achieved in stages with the proviso that the conditions of alkylation are less severe in the initial alkylation stage than in a secondary stage, e.g., through the use of a lower temperature in the first stage as opposed to a higher temperature in a secondary stage.
U.S. Pat. No. 6,059,962 in the name of Bruce D. Alexander, George A. Huff, Vivek R. Pradhan, William J. Reagan and Roger H. Clayton disclosed A product of reduced sulfur content is produced in a multiple stage process from a feedstock which is comprised of a mixture of hydrocarbons and includes sulfur-containing aromatic compounds as unwanted impurities. The first stage involves: (1) subjecting the feedstock to alkylation conditions which are effective to convert a portion of the impurities to higher boiling sulfur-containing products, and (2) separating the resulting products by fractional distillation into a lower boiling fraction and a higher boiling fraction. The lower boiling fraction is comprised of hydrocarbons and is of reduced sulfur content relative to the feedstock. The higher boiling fraction is comprised of hydrocarbons and contains unconverted sulfur-containing aromatic impurities and also the higher boiling sulfur-containing products. Each subsequent stage involves: (1) subjecting the higher boiling fraction from the preceding stage to alkylation conditions which are effective to convert at least a portion of its content of sulfur-containing aromatic compounds to higher boiling sulfur-containing products, and (2) separating the resulting products by fractional distillation into a lower boiling hydrocarbon fraction and a higher boiling fraction which contains higher boiling sulfur-containing alkylation products. The total hydrocarbon product of reduced sulfur content from the process is comprised of the lower boiling fractions from various stages. Again it is stated that alkylation can be achieved in stages with the proviso that the conditions of alkylation are less severe in the initial alkylation stage than in a secondary stage, e.g., through the use of a lower temperature in the first stage a opposed to a higher temperature in a secondary stage.
There is, therefore, a present need for catalytic processes to prepare products of reduced sulfur content from a feedstock wherein the feedstock is comprised of limited amounts of sulfur-containing and/or nitrogen-containing organic compounds as unwanted impurities, in particular, processes which do not have the above disadvantages. A further object of the invention is to provide inexpensive processes for the efficient removal of impurities from a hydrocarbon feedstock.
An improved process should be an integrated sequence, carried out in the liquid phase using a suitable alkylation-promoting catalyst system, preferably an alkylation catalyst capable of enhancing the incorporation olefins into sulfur-containing organic compounds thereby assisting the removal of sulfur or nitrogen from a mixture of organic compounds suitable as blending components for refinery transportation fuels liquid at ambient conditions.
Advantageously, an improved desulfurization process shall minimize formation of unwanted co-products, such as formation undesired oligomers and polymers from the polymerization of olefinic alkylating agents. Beneficially, an improved desulfurization process shall efficiently remove sulfur-containing impurities from an olefinic cracked naphtha, but does not significantly reduce the octane rating of the naphtha.
This invention is directed to overcoming the problems set forth above in order to provide components for refinery blending of transportation fuels friendly to the environment.
Economical processes are disclosed for the production of components for refinery blending of transportation fuels by integrated, multiple stage, selective sulfur removal through alkylation by olefins. This invention contemplates the treatment of various type hydrocarbon materials, especially hydrocarbon oils of petroleum origin which contain sulfur. In general, the sulfur contents of the oils are in excess of 1 percent, and range up to about 2 or 3 percent. Processes of the invention are particularly suitable for treatment of a refinery feedstream comprised of gasoline, kerosene, light naphtha, heavy naphtha, and light cycle oil, and preferably a naphtha from catalytic and/or thermal cracking processes.
Multiple stage sulfur removal processes of the invention involve the use of an initial alkylation zone and at least one subsequent alkylation zone which is operated at less severe conditions than the initial alkylation zone. Beneficially, the products formed contain organic sulfur compounds of higher molecular weight than corresponding mercaptans, sulfides and sulfur-containing aromatics, such as thiophenic and benzothiophenic compounds, in the feedstock.
In one aspect, this invention provides a process for the production of products which are liquid at ambient conditions and contain organic sulfur compounds of higher molecular weight than corresponding sulfur-containing compounds in the feedstock, which process comprises; (a) providing a feedstock comprising a mixture of hydrocarbons which includes olefins and sulfur-containing organic compounds, the feedstock consisting essentially of material boiling between about 60xc2x0 C. and about 345xc2x0 C. and having a sulfur content up to about 4,000 or 5,000 parts per million, (b) in an initial contacting stage at elevated temperatures, contacting the feedstock with an acidic catalyst under conditions which are effective to convert a portion of the impurities to a sulfur-containing material of higher molecular weight through alkylation by the olefins, thereby forming an initial product stream; and (c) in a subsequent contacting stage and at temperatures of at least 10xc2x0 C. lower than an average of the elevated temperatures in the initial contacting stage, contacting at least a portion of the initial product stream with an acidic catalyst under conditions which are effective to convert a portion of the impurities to a sulfur-containing material of higher molecular weight through alkylation by the olefins, thereby forming a subsequent product stream.
In another aspect, this invention provides a process for the production of products which are liquid at ambient conditions and have a reduced sulfur content relative to the feedstock, which process comprises; (a) providing a feedstock comprising a mixture of hydrocarbons which includes olefins and sulfur-containing organic compounds, the feedstock consisting essentially of material boiling between about 60xc2x0 C. and about 345xc2x0 C. and having a sulfur content up to about 4,000 or 5,000 parts per million, (b) in an initial contacting stage at elevated temperatures, contacting the feedstock with an acidic catalyst under conditions which are effective to convert a portion of the impurities to a sulfur-containing material of higher boiling point through alkylation by the olefins, thereby forming an initial product stream, (c) in a subsequent contacting stage and at temperatures at least 10xc2x0 C. lower than an average of the elevated temperatures in the initial contacting stage, contacting at least a portion of the initial product stream with an acidic catalyst under conditions which are effective to convert a portion of the impurities to a sulfur-containing material of higher boiling point through alkylation by the olefins, thereby forming a subsequent product stream, and (d) fractionating the subsequent product stream by distillation to provide (i) at least one low-boiling fraction consisting of a sulfur-lean fraction having a sulfur content less than about 50 ppm, and (ii) a high-boiling fraction consisting of a sulfur-rich, fraction containing the balance of the sulfur. In preferred embodiments of invention the multistage process provides a low-boiling fraction which has a sulfur content of less than about 30 parts per million. More preferred are embodiments which provide products which have a sulfur content of less than about 15 parts per million, and most preferably less than about 10 parts per million.
Other aspects of the invention include compositions formed by any process disclosed herein. Such compositions have a sulfur content of less than about 50 parts per million, preferably less than about 30 parts per million, more preferably have a sulfur content of less than about 15 parts per million, and most preferably less than about 10 parts per million.
Suitable feedstocks include products of refinery cracking processes which consists essentially of material boiling between about 200xc2x0 C. and about 425xc2x0 C. Preferably such refinery stream consisting essentially of material boiling between about 220xc2x0 C. and about 400xc2x0 C., and more preferably boiling between about 275xc2x0 C. and about 375xc2x0 C. Where the selected feedstock is a naphtha from a refinery cracking process, the feedstock consists essentially of material boiling between about 20xc2x0 C. and about 250xc2x0 C. Preferably the feedstock is a naphtha stream consisting essentially of material boiling between about 40xc2x0 C. and about 225xc2x0 C., and more preferably boiling between about 60xc2x0 C. and about 200xc2x0 C.
Beneficially for processes of the invention the feedstock is comprised of a treated naphtha which is prepared by removing basic nitrogen-containing impurities from a naphtha produced by a catalytic cracking process. Preferably, the olefin content of the feedstock is at least equal on a molar basis to that of the sulfur-containing organic compounds.
According to the invention, the acidic catalyst of initial contacting stage is the same or different from that of the subsequent contacting stage. Advantageously a solid phosphoric acid catalyst is used as the acidic catalyst in at least one of the contacting stages.
Beneficially the temperatures used in the subsequent contacting stage are at least 5xc2x0 C. lower than an average of the elevated temperatures in the initial contacting stage. The temperature differential between the initial alkylation stage and the subsequent stage preferably is in a range of from about negative 5xc2x0 C. to about negative 115xc2x0 C., more preferably in a range from about negative 15xc2x0 C. to about negative 75xc2x0 C. Where a solid phosphoric acid catalyst is used as the acidic catalyst in at least one of the contacting stages, the temperatures used in the subsequent contacting stage is preferably at least 25xc2x0 C. lower than an average of the elevated temperatures in the initial contacting stage, and more preferably at least 45xc2x0 C. lower.
In one aspect of this invention the elevated temperatures used in the initial contacting stage are in a range from about 120xc2x0 C. to about 250xc2x0 C. Where a solid phosphoric acid catalyst is used as the acidic catalyst in an initial contacting stage, the elevated temperatures are preferably in a range of temperature from about 140xc2x0 C. to about 220xc2x0 C., and more preferably in a range from about 160xc2x0 C. to about 190xc2x0 C. Where a solid phosphoric acid catalyst is used as the acidic catalyst in both stages of contacting, the temperatures in the subsequent stage are preferably in a range of temperature from about 90xc2x0 C. to about 250xc2x0 C., preferably at temperatures in a range from about 100xc2x0 C. to about 235xc2x0 C., and more preferably at temperatures in a range from about 110xc2x0 C. to about 220xc2x0 C.
In one aspect of this invention the temperature cut-point in distillation step separating the low-boiling fraction and the high-boiling fraction is in the range from about 70xc2x0 C. to about 200xc2x0 C., and preferably in the range from about 150xc2x0 C. to about 190xc2x0 C. Advantageously, the high-boiling fraction has a distillation end point which is below about 249xc2x0 C.
In another aspect, this invention provides one low-boiling fraction having a distillation end point and a high-boiling fraction having an initial boiling point such that the distillation end point and the initial boiling point are in the range from about 80xc2x0 C. to about 220xc2x0 C.
In yet another aspect, this invention provides a process for the production of products which are liquid at ambient conditions and have a reduced sulfur content relative to the feedstock, which process comprises; (a) providing a feedstock comprising a mixture of hydrocarbons which includes olefins and sulfur-containing organic compounds, the feedstock consisting essentially of material boiling between about 60xc2x0 C. and about 345xc2x0 C. and having a sulfur content up to about 4,000 or 5,000 parts per million, (b) in an initial contacting stage at elevated temperatures, contacting the feedstock with an acidic catalyst under conditions which are effective to convert a portion of the impurities to a sulfur-containing material of higher boiling point through alkylation by the olefins, thereby forming an initial product stream, (c) in a subsequent contacting stage and at temperatures at least 10xc2x0 C. lower than an average of the elevated temperatures in the initial contacting stage, contacting at least a portion of the initial product stream with an acidic catalyst under conditions which are effective to convert a portion of the impurities to a sulfur-containing material of higher boiling point through alkylation by the olefins, thereby forming a subsequent product stream, (d) fractionating the subsequent product stream by distillation to provide at least one low-boiling fraction consisting of a sulfur-lean, mono-aromatic-rich fraction having a sulfur content less than about 50 ppm, and a high-boiling fraction consisting of a sulfur-rich, mono-aromatic-lean fraction containing the balance of the sulfur, (e) treating the high-boiling fraction with a gaseous source of dihydrogen at hydrogenation conditions in the presence of a hydrogenation catalyst which exhibits a capability to enhance the incorporation of hydrogen into one or more of the sulfur-containing organic compounds and under conditions suitable for hydrogenation of one or more of the sulfur-containing organic compounds, and (f) recovering a high-boiling liquid having a sulfur content less than about 50 ppm. Advantageously, all or a portion of the a high-boiling liquid is blended with at least one low-boiling fraction of the distillation.
In a further aspect of this invention, the hydrotreating of the petroleum distillate employs at least one bed of hydrogenation catalyst comprising one or more metals selected from the group consisting of cobalt, nickel, molybdenum and tungsten.
Advantageously, the contacting the high-boiling feedstock with a gaseous source of dihydrogen employs at least one bed of hydrogenation catalyst comprising one or more metals selected from the group consisting of nickel, molybdenum and tungsten.
Generally, useful hydrogenation catalysts comprise at least one active metal, selected from the d-transition elements in the Periodic Table, each incorporated onto an inert support in an amount of from about 0.1 percent to about 30 percent by weight of the total catalyst. Suitable active metals include the d-transition elements in the Periodic Table elements having atomic number in from 21 to 30, 39 to 48, and 72 to 78.
Useful catalyst for the hydrotreating comprise a component capable to enhance the incorporation of hydrogen into a mixture of organic compounds to thereby form at least hydrogen sulfide, and a catalyst support component. The catalyst support component typically comprises a refractory inorganic oxide such as silica, alumina, or silica-alumina. Refractory inorganic oxides, suitable for use in the present invention, preferably have a pore diameter ranging from about 50 to about 200 Angstroms, and more preferably from about 80 to about 150 Angstroms for best results. Advantageously, the catalyst support component comprises a refractory inorganic oxide such as alumina.
Hydrotreating of the refinery distillate preferably employs at least one bed of hydrogenation catalyst comprising cobalt and one or more metals selected from the group consisting of nickel, molybdenum and tungsten, each incorporated onto an inert support in an amount of from about 0.1 percent to about 20 percent by weight of the total catalyst.
Contacting of the high-boiling fraction with a gaseous source of dihydrogen preferably employs at least one bed of hydrogenation catalyst comprising nickel and one or more metals selected from the group consisting of, molybdenum and tungsten, each incorporated onto an inert support in an amount of from about 0.1 percent to about 20 percent by weight of the total catalyst.
This invention is particularly useful towards sulfur-containing organic compounds in the oxidation feedstock which includes compounds in which the sulfur atom is sterically hindered, as for example in multi-ring aromatic sulfur compounds. Typically, the sulfur-containing organic compounds include at least sulfides, heteroaromatic sulfides, and/or compounds selected from the group consisting of substituted benzothiophenes and dibenzothiophenes.
Hydrogenation catalysts beneficially contain a combination of metals. Preferred are hydrogenation catalysts containing at least two metals selected from the group consisting of cobalt, nickel, molybdenum and tungsten. More preferably, co-metals are cobalt and molybdenum or nickel and molybdenum. Advantageously, the hydrogenation catalyst comprises at least two active metals, each incorporated onto a metal oxide support, such as alumina in an amount of from about 0.1 percent to about 20 percent by weight of the total catalyst.